A former congressman is attempting a comeback by appealing to an unconventional bloc of GOP primary voters: moderates.

And that's not even strangest thing about former Rep. Todd Tiahrt's campaign to oust his successor, GOP Rep. Mike Pompeo, on Aug. 5. With the help of one of Pompeo's former foes, wealthy oilman Wink Hartman, Tiahrt is taking on his one-time backers and the GOP's ultimate Goliath, the Koch brothers, in their own backyard.

Tiahrt's eleventh-hour bid comes four years after he lost a bitter Senate primary to now-Sen. Jerry Moran. After that, the former eight-term appropriator endorsed Pompeo — twice.

Then there's the ex-congressman's message: Tiahrt is running to the left of Pompeo, striking a populist tone in the conservative district.

"It's tough to get to 50 [percent] that way in a Republican primary in the 4th District of Kansas," said David Kensinger, a former chief of staff to Kansas Republican Gov. Sam Brownback.

For example, in a phone interview last week with CQ Roll Call, Tiahrt accused Pompeo of “crony capitalism” by introducing legislation that would allow the federal government to determine labeling standards for genetically modified foods, instead of state governments. Some of the most liberal members of Congress, including Sen. Bernard Sanders, I-Vt., have opposed the legislation .

Tiahrt also argues Pompeo hasn't done enough to help the aviation industry — one of the biggest job producers in the area.

“We’ve lost half of our airplane companies in Wichita since Mr. Pompeo came to Congress,” Tiahrt told CQ Roll Call. “We’re now becoming the Detroit of aviation, and that’s because he hasn’t been there to fight for them. He’s off jet setting around the globe going to destination fundraisers.”

Pompeo's campaign says Tiahrt's claims range from misleading to false, pointing to a similar genetically modified foods bill Tiahrt co-sponsored in 2006 . Pompeo added that he's been a strong supporter of the aviation industry during his three years in Congress.

But most of all, Pompeo said he is perplexed by Tiahrt’s attacks, which represent a 180-degree turn from the praise he offered Pompeo in his previous runs. In 2010, Tiahrt endorsed Pompeo’s bid, saying he would “sleep well at night” if he succeeded him in Congress. Two years later, Tiahrt applauded Pompeo for aiding the aviation industry.

"All I can say is I haven’t changed one whipstitch," Pompeo said in a July 25 phone interview. "I'm convinced he won't fool them, but I will say it’s bad for our Republic when a 16-year member of Congress believes he can just say anything to get back to Washington, D.C."

Tiahrt’s flip baffles other Jayhawk State Republicans, who privately question the motivations behind his last-minute campaign. They speculate Tihart could be trying to build name identification for another statewide bid or ponder whether one of Pompeo’s adversaries pushed the former congressman to run. Maybe Tiahrt just wanted a new gig.

No matter his motivation, GOP operatives say Tiahrt's path to victory is a tough one.

But a poll conducted for Pompeo's campaign and provided to CQ Roll Call found Pompeo with a wider lead over Tiahrt, 45 percent to 26 percent. That poll surveyed 400 likely primary voters via live telephone calls July 21-23. It was conducted by CMA Strategies and had a margin of error of 4.9 points.

What's more, some of Tiahrt's biggest financial supporters during his congressional tenure are now backing Pompeo.

After stuffing Tiahrt's war chest with more than $300,000 over his 16-year congressional career, Koch Industries now supports Pompeo, according to the Center for Responsive Politics.

David Koch maxed out to Pompeo, contributing $5,200 to his campaign. Koch Industry employees are also the biggest contributor to Pompeo's war chest, donating $46,000 this cycle alone, according to the CRP. The company's political action committee also contributed $10,000 to Pompeo, the maximum amount allowed under federal campaign law.

Two weeks from the primary, Americans for Prosperity, Charles and David Koch's 501(c)4 advocacy group, is up on air with an ad praising Pompeo's conservative chops.

The incumbent is taking the challenge seriously too. He's been up on air touting his conservative record and currently airing an ad responding to Tiahrt's attacks.

"How can you tell when Todd Tiahrt is saying something false or misleading about Mike Pompeo? Well you could say it's when his lips are moving," a narrator says in a minute-long contrast spot. "Evidently Todd Tiahrt will say anything to get back to his home in Washington."

Whoever wins the GOP primary is the heavy favorite to keep the seat in November. Kansas' 4th District is rated a Safe Republican contest by the Rothenberg Political Report/Roll Call.